The presence of microbial growth can cause bio-fouling and plugging of wells. Such plugging can occur both in vadose-zone wells and in saturated-zone wells. Vadose-zone wells are wells having a well bore that does not extend into the water table, and include, for example, vadose-zone monitoring wells, vapor extraction wells and injection wells. Saturated-zone wells have a well bore that extends into the water table such as, for example, ground water monitoring wells, production wells and irrigation wells. Plugging of a well may occur by plugging of structures within the well such as the filter pack, screening, piping, or pumps. Plugging may also occur by the plugging of the surrounding geological media. Such plugging is caused by an accumulation of microbial growth, by an accumulation of microbial extracellular material, or both.
Once a well has become bio-fouled or plugged, treatment of the well to eliminate microbial growth and remove plugging is often difficult and ineffective. Remedial chemical treatments, such as an introduction of a highly concentrated chlorine solution into the well, often fail due to the difficulty in forcing the solution through an already plugged well. Once bio-fouling has occurred, replacement of the effected structure is often required. Severe bio-fouling and plugging may require replacement of the entire well at great expense.
Accordingly, it is desirable to provide well constructions and preventative treatment methods designed to minimize unwanted microbial growth in wells.